I have been using Firefox 4.0, and my add on extensions for Flashgot, Free Download Manager, No Script, all worked well. I upgraded to Firefox 5.7 and all went wrong. All extensions disappeared, so i added on again for FDM and No Script, (Flashgot has not extension for Quantum, that is fine, and I know that). The rest seemed to work, but after I restart Firefox, all extensions disappeared. Logitech Setpoint kept appearing as in error, that could be because Quantum is not happy with Logitech mouse T400. I uninstalled Firefox 5.7, and uninstalled Firefox 4.0 (there is a version Firefox 3.0 that I left alone since, it was upgraded two versions already). Firefox 4.0 was reinstalled, and working well, and I add on Flashgot extension and it worked beautifully. However, FDM add on cannot be installed, with error and retry error. I took malware out, deleted pref. , deleted extension. files; deleted cache; FDM add on error again. Refreshed, reset, etc. all done, same problem. Other add on are also fine and working. Also, how do I delete extension error message for Logitech Setpoint after I already removed the extension item. Kept appearing with no option to delete or remove.